Google says that "jättetrötta" is a "giant tire", but if it was singular "jag är jättetrött" it would work, right? will it work with plural as well? does it work at all? :)
Jätte- literally means giant and is a very common ’prefix’ meaning very. You could use it just like you did in both the singular (jättetrött) and the plural (jättetrötta).